In U.S. Pat. No. 4,679,396 of one of the inventors, William S. Heggie, corresponding to United Kingdom patent No. 2,065,836 (granted May 10, 1984) there is described a hydraulic transmission system which has been used successfully for vehicles. In that system two variable displacement hydraulic pump units are used and a hydraulic unit is coupled to the engine.
In other proposed systems two or more hydraulic pumps are used as well as a relatively large number of hydraulic components, one connected to the engine and one connected to the wheels through a clutch arrangement--see, for example, the description of a VOLVO system in the United Kingdom publication "The Automotive Engineer" April/May 1986, page 20.